Underground liquefaction of coal



May 6, 1952 E. F. PEVERE ET Al. 2,595,979

UNDERGROUND LIQUEFACTION OF COAL Filed Jan. 25, 1949 Patented May 6,1952 UNITED STATES PATENT ofi-Fics UNDERGROUND LIQUEFACTION OF COALErnest. F'. Revere,` Beacon, and Georgev vB. Arnold,

Glenham.. N.v Y.,. assignors to The Texas Company; New York, N. Y., acorporation of Del- Application January 25, 1949, Serial N o. 72,582`

( Cl. 19E-53) 2' Claims. l.

` This invention relatestoa process for the recovery of coal substancefrom. underground deposits in the formv of a liquid In oneof. its morespecific aspects, this invention relates tov the undergroundIiquefaction oi. a liqueable fraction. of a coal deposit. byhydrogenation to produce a liquid extract suitable for use in the.production ofmotor fuels.

In accordance with the present invention, coal in an underground depositis hydrogen-ated in situ by contact with a. hydrogenating agent. Thehydrogenation is carried out. at an elevated temperature and pressure,which may be controlled from above ground. The. hydrogenation reactionproduces a liquid product which is readily recovered` as a relativelyheavy oil. The crude liquid product may be subject to furtherhydrogenation and refining operations. to produce motor fuels and otherdesired products after recovery from the undergroundformation.

The hydrogenating. agent used in the present process may be freehydrogen or an organic compound capable of liberating hydrogen.Hydroaromatics, such as hydrogenated naphthalenes, e. g., tetralin anddecalin, and heavy oils obtained by hydrogenation of` coal are suitablehydrogenating agents. Hydroaromatic oils act as solvents in theliquefaction of coal, due primarily to their ability to transferhydrogen to the coal.

In general, from about 70 to about 90 per cent by weight of avbituminous coal may be liqueed by hydrogenation, the extent of theliquefaction depending largely upon the grade of the coal. Approximately65 per cent by weight of massive or lump coal may be readilyA liquefied'by hydrogenation. The hydrogen consumption' generally' ranges from about1.5 to about 3 percent by weight based on the Weight of the coalreacted. The liqueed coal, or extract, obtained on hydrogenation isfluid and substantially free from ash.

This liquid may be recovered from thefcoal seamY by the process of thisinvention in a manner analogous to the. production. of crude oil. Theresidual or unhydrogenated portion of the coal comprises unreactedcarbon and the mineral matter or ash. The residue may also. be utilizedadvantageously as will be brought out hereinafter.

The process of the present invention has many advantages over priormethodsof producing hydrocarbons from coal.` The methods. of the priorart include conventional hydrogenationa of powdered coal, and methodsfor thev gasication of coal to produce a mixture of carbon monoxideandhydrogen followed by conversion of the carbon monoxide and hydrogen toliquidv hydrocarbons by theFischer-Tropsch synthesis.

In the conventional coal hydrogenation process, the coal is mined in theusual manner.. dried, pulverized and made into a paste by. admixing thepowdered coal with a heavy oil. The paste is mixed with hydrogen and.reacted at a temperature of from about 800 to about 900' F. and atpressures ranging from about 43000. to about 10,000 pounds per squareinch.

An important elementr of cost in conventional coal hydrogenati'onprocesses is. the cost .of preparation of the coal for hydrogenation.The. ne grinding of the coal to obtain a. powder requires theexpenditure of large amounts of' power. In addition, costly high.pressure. reactors, pumps, transfer lines and related equipment. arerequired.

The mining of bituminous coal., for. example, is in itself a wasteful.procedure. It has been. estimated that on an overall average,v about percent of the coal in place is recovered from the mines, the remainderbeing left, as supporting pillars, etc. There is another l0 per. centvloss incurred in the handlingoperations so. that` only about 55 per centof. thecoal in place is recovered as marketable coal. In addition, a.considerable amount of methane is lost. from` every ton of coalproduced. Contact with atmosphericA oxygen results in some chemical.reaction.. rendering the coal somewhat less reactive for hydrogenation.

than is the virgin coal. The recovery of. coal substance from the.deposit iby the-present. process is, therefore, comparable in eiliciencyto modern mining methods..

The. present process does not. suffer from the depth limitations whichare. imposed upon mining operations. At4 adepth of 5,000 feet.. forexample, the temperature of' the. earths. crust is about, F'., whichmakes. the cost @airconditioning and Ventilating the coal seams too.4expensive to work them by conventional mining. methods. Such undergroundtemperatures. are an advantage of the process of the present. invention.

Another. important. advantage of this invention derives from the factthat. the unhydrogenated portion of the coal seam is left in a porous orhoneycomb state whichv is. almost ideallyl suited for undergroundgasification. The present invention also contemplates recovery of carbonvalues from the unhydrogenated residue by gasication of the residue.` insituA by contact with an oxygen-containing gas. cation of coal with anoxygen-containing gas is already known inthe art.. Much diiculty hasbeen experienced with previous methods of gasication due to the fact.that a. complicated system of passagevvays must rst be provided throughthe coal seam to permit passage of the oxidizing gases therethrough.. Inthe present process, the passageways. are provided by the removal of thehydrogenatable. portion of the coal so that a pervious massiefreactivecarbonaceous material remains for the gasication reaction. Theoxygen-containing. gas mayv be passed directly through thisresidue-without' the4 Underground gasinecessity of drilling passagewaystherethrough.

An object of the present invention is to provide an improved process forthe recovery of coal from underground deposits.

Another object is to provide a process for the liquefaction of coalsubstances in underground seams.

Still another object is to provide an improved process for recovery ofcoal as a liquid from underground deposits.

Another specific object is to provide an improved method of recovery ofcoal from underground deposits, partly as a liquid hydrogenation productand partly as a gaseous product of underground gasification.

Other objects and advantages will be apparent to those skilled in theart from the following detailed description.

In the process of this invention, coal is liquefied at a temperatureabove about 550 F. and generally within the range of from about 550 toabout 850 F. by direct contact between the virgin coal and thehydrogenating agent. Preferably the temperature is maintained within therange of 700 to 750 F. Pressures above about 1,000 pounds per squareinch are suitable. The pressure may range up to about 10,000 pounds persquare inch where such pressures may be used without excessive loss ofhydrogen due to leakage from the coal seam. Structural limitationsusually require the use of pressures in the lower portion of this range;higher pressures are desirable wherever practical.

The rate of reaction, and the reaction temperature, may be controlled bycontrol of the pressure at which the reaction is carried out. As thepressure is increased, the rate of reaction and the reaction temperatureincrease; as the pressure is decreased, the rate and temperaturedecrease.

In carrying out the present process, a well bore is drilled into thecoal seam through which the hydrogenating agent may be admitted and theresulting liquid product withdrawn. The hydrogenating agent is forcedunder pressure through the well bore into direct contact with the virgincoal in the underground seam. Gaseous hydrogen is preferable as thehydrogenating agent. The hydrogen permeates the residue relativelythoroughly and produces by reaction with the coal an oil which is anexcellent solvent and hydrogen transfer agent. The heavy oil orliquefied coal substance obtained by hydrogenation is one of the besthydrogen carriers known at the present time. The hydrogen diffusesupwardly into the coal seam, liquefying the more readily liqueable coalsubstance. This liquid then drains down over the less readilyliquefiable portion of the coal, thus acting as a hydrogen carrier tofacilitate the liquefaction.

The reaction is initiated by raising the temperature at the coal face tothe reaction temperature.

Any means of supplying heat may be used; preferable are those involvingliberation of heat near the face of the coal seam by chemical means. Anelectrical heater may be placed in the well bore to preheat thereactants. Superheated vapors of a hydroaromatic may thus be supplied tothe coal whereupon heat is transferred to the coal upon condensation ofthe vapors to supplement the heat liberated by the reaction. Onceinitiated, the exothermic heat of reaction and the heat transfer betweenthe reactants and reaction products serve to maintain the reactiontemperature.

The `well bore is preferably drilled into a low portion of the coal seamto permit the liquid product to drain down to the well bore for removal.The process is well adapted to working those seams which are inclined atan angle too steep for conventional mining. The process is particularlyadapted to working those coal seams which are overlain by a relativelyimpervious stratum. Generally, the coal seams are overlain with a layerof clay and shale which is relatively impervious and is a good heatinsulator.

The loss of hydrogen into pervious adjacent formations may often belargely eliminated by operating at high temperatures for a period oftime such that some of the fusible metal salts in the formations aremelted or some of the volatile metal salts associated with the coal arevaporized, thus plugging the walls of the adjacent formation. Thetemperature may be increased by operating at very high pressure toincrease the rate of reaction and hence the rate of heat at which heatis liberated by the exothermic heat of reaction. Volatile metals may besupplied to the coal seam in the form of a concentrated solution of asoluble salt of one of the metals during the course of reaction. Halidesof zinc and lead, for example, are suitable for this purpose.

A typical product obtainable by underground hydrogenation comprises 60to 70 per cent liquid hydrocarbons and l0 to 30 per cent gaseoushydrocarbons. About 31/2 to 4 barrels of oil are obtained from each tonof coal reacted. Approximately 27 per cent of the liquid hydrocarbonfraction has a boiling range within the gasoline range that is up to 392F., 50 per cent between 392 and 572 F. and 23 per cent above 572 F.

A solvent extraction, based on hydrogenation by hydrogen transfer, maybe carried out by using one of the liquid hydrogenating agents forrecovery of the coal. Among the hydrogenating agents which are suitablefor this purpose are tetrahydro-naphthalene, decahydro-naphthalene,crude cresols, oil from the hydrogenation of coal, aromatic crude oil,and the like. Preferably the liquid hydrogenating agent is supplementedwith gaseous hydrogen. The liquid hydrogenating agent may be injectedinto the coal seam and recovered therefrom either intermittently orcontinuously. The liquid hydrogenating agent may be injected into theupper part of the seam and the liquid product recovered from a lowerportion of the seam. Appropriate passages may be provided in the coalseam for injection of the hydrogenating agent and recovery of theproduct. A portion of the product, preferably a heavy fraction, may beused effectively as the hydrogenating agent, most suitably afterhydrogenation aboveground.

Often the coal seam is pervious due to structural anomalies, sometimesresulting from foi'- ing or faulting of the strata. The permeability ofthe coal may be increased by dissolution of part or all of the mineralmatter, thus opening pores in the coal. A concentrated mineral acid,preferably sulfuric acid, may be used for this purpose.

A catalyst may be used for the hydrogenation reaction. Iodine is aneffective catalyst for this purpose. The iodine may be employed ineither the elemental state, as hydrogen iodide, or in the form of anorganic compound of iodine, e. g., methyl iodide, iodoform, methyliodoform, etc.

The accompanying drawing illustrates diagrammatically the process ofthis invention.

With reference to the drawing, the numeral i designates an undergroundseam of coal above which is a relatively impervious stratum 2, generallyof clay and shale, and below which is another relatively imperviousstratum 3, e. g., a layer of clay. A well bore is drilled from thesurface of the earth #i to a low point in the coal seam adjacent theunderlying stratum `3. Separate conduits 5 and 6 extend through the wellbore into the coal seam. These conduits may be placed in any convenientmanner analogous to the placement of tubing and casing in oil wells. Asillustrated in the drawing, conduit 6 is placed within conduit 5 leavingan annular passageway 'l therebetween.

An enlarged cavity 8 may be formed at the terminus of the Well bore toserve as a collection chamber for liquefied coal. The conduit 5preferably is closed at its lower end and provided with a number ofperforations 9 adjacent the coal stratum as outlets for thehydrogenating agent. The hydrogenating agent is admitted to conduit 5through pipe I6, flowing through the annular passageway 'l and theperforations 9 into the coal stratum. The liqueed coal or liquidhydrogenation product is withdrawn through pipe 6.

As the hydrogenation progresses, a porous, honeycomb-like residue i2 isleft in place in the formation. The liquid resulting from theliquefaction drains away from the residue, collects in the cavity 8 andflows through pipe 6 to the surface where it may be subjected toappropriate refining methods.

Obviously, a plurality of well bores may be employed in carrying out theprocess, with injection of the hydrogenating agent into one or morewells and recovery of the liquefied coal from one or more additionalwells. The well may be used alternately for injection and recovery,either alone or in combination with other wells.

The crude product comprises not only the liquid and gaseous hydrocarbonsbut also tar acids, tar bases, ammonia, carbon dioxide, carbon monoxide,water, and hydrogen sulfide. The crude product is preferably maintainedunder an elevated pressure of at least 100 pounds per square inch untila separation of the oil and water layers has been effected at thesurface of the earth.

In this way, most of the carbon dioxide, ammonia and hydrogen sulfideremain in the water layer, the ammonia in the form of salts of carbondioxide or hydrogen sulde.

After the separation of the Water layer, the pressure is released topermit the escape of the excess carbon dioxide from the water fraction.The ammonia may then be recovered by makingf the water layer alkalineand heating the water layer to release the ammonia. Ammonium carbonatemay be produced by combining the recovered ammonia with some of thecarbon dioxide originally released from the water layer. Sulfur may alsobe obtained as a by-product by oxidation of the hydrogen sulde in aneutral solution by blowing with air and recovering the resulting sulfurfrom the water layer by filtration.

The hydrocarbon gases and carbon monoxide dissolved in the liquidhydrocarbon product are separated by stabilization and these gases usedfor the liquefaction process. Hydrogen from any suitable source may beemployed in the process.

The stabilized hydrocarbon may be treated to remove the tar acids andthe tar bases. The tar acids are suitably removed by a caustic wash andthe tar bases by an acid wash, as is known in the art. Tar acids andbases may be recovered from the resulting solutions by neutralizing andskimming although it is sometimes desirable to extract the neutralsolution with a suitable sol- 'vent such as ether, acetone, or the like.The tar acids and bases may be separated into various constituentcompounds by conventional methods or, as is often the case, sold andused as mixtures.

After removal of the tar acids and bases, the residual stabilizedhydrocarbons may be separated into the usual fractions by distillationand by other refining methods. The hydrocarbon fraction containsrelatively large quantities of aromatic constituents. In some instances,it may be desirable to separate some of these materials for chemicaluses.

Obviously many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof and, therefore, only such limitations should beimposed as are indicated in the appended claims.

Vle claim:

. 1. A process for the recovery of coal from underground deposits whichcomprises contacting the coal in situ with a hydrogenating agentselected from the group consisting of free hydrogen and hydroaromaticcompounds at a temperature within the range from about 550 F. to about850 F. and a pressure above about 1,000 pounds per square inch gaugeeffective tohydrogenate a portion of the coal substance to form aliquid, and recovering the resulting liqueed coal substance from theunderground deposit.

2. A process for the recovery of coal substance from a subterranean coaldeposit which comprises drilling a well bore from the surface of theearth into the coal seam, introducing hydrogen through the well boreinto Contact with the coal in situ at a pressure above about 1,000pounds per square inch gauge,'initiating the reaction between hydrogenand coal in said deposit by heating the coal in the area adjacent thewell bore to a temperature above about 550 F. whereby hydrogen combineswith a portion of the coal substance to form a liquid, maintaining thetemperature within the range of from about 550 to about 850 F.,collecting the resulting liquefied coal substance in a well bore,withdrawing said liquid from the subterranean deposit through a wellbore.

ERNEST F. PEVERE. GEORGE B. ARNOLD.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 345,586 Hall July 13, 1886947,608 Betts Jan. 25, 1910 1,532,826 Lessing Apr. 7, 1925 1,669,439Bergius May 15, 1928 2,039,459 Seguy May 5, 1936 2,119,647 Pier et alJune 7, 1938 2,165,940 Pier et al. July 11, 1939 2,177,376 Pier et alOct. 24, 1939

1. A PROCESS FOR THE RECOVERY OF COAL FROM UNDERGROUND DEPOSITS WHICHCOMPRISES CONTACTING THE COAL IN SITU WITH A HYDROGENATING AGENTSELECTED FROM THE GROUP CONSISTING OF FREE HYDROGEN AND HYDROAROMATICCOMPOUNDS AT A TEMPERATURE WITHIN THE RANGE FROM ABOUT 550* F. TO ABOUT850* F. AND A PRESSURE ABOVE ABOUT 1,000 POUNDS PER SQUARE INCH GAUGEEFFECTIVE TO HYDROGENATE A PORTION OF THE COAL SUBSTANCE TO FORM ALIQUID, AND